The present invention relates to a method of making optical devices such as fiber optic components and integrated optical components of the type from which there extend short lengths of optical fibers referred to herein as "pigtails". Such optical devices can perform such functions as coupling, wavelength division multiplexing, filtering and the like. Couplers are discussed herein by way of example in order to provide an understanding of the background of the present invention.
Reproducible methods of making rugged optical fiber couplers are disclosed in published European patent application No. 0302745, published 08 Feb. 89. A plurality of suitably prepared glass fibers, each having a core and cladding, are disposed within the longitudinal aperture of a glass capillary tube. Each fiber extends beyond at least one end of the tube to form a connection pigtail. The pigtails are provided with the same type and diameter of coating as the optical fibers of the system in which the device is intended to be used so that the device can be easily integrated into the system. The midregion of the tube is heated and collapsed about the fibers, and the central portion of the collapsed midregion is stretched to reduce the diameter thereof. The optical fibers used to form the coupler are conventionally provided with a plastic coating to increase the strength and/or the handleability thereof. The preparation of the optical fibers has involved removing the coating from that portion of the fiber which is positioned at the midregion of the tube. The coated portion of a fiber is pulled through the tube aperture in order to position the bared region in the center of the tube prior to the tube collapse step. In one prior art embodiment, the coated portions of each fiber extend into the ends of the tube aperture to hold the fibers in proper alignment while the tube is collapsed thereon. The aperture must therefore be large enough to accept the coated portions of the fibers. If air is trapped adjacent the fibers or if glass flows between the fibers during the tube collapse step, optical characteristics such as attenuation and coupling ratio are adversely affected. These adverse effects are more likely to occur when the aperture diameter is relatively large, whereby the tube must undergo an inordinate amount of collapse prior to the time that it engages the fibers therein.
Another optical device to which the present invention pertains is the integrated optical component, which comprises optical waveguide paths on or in the surface of a substrate. Such devices can function as signal splitters, single-mode proximity couplers, single-mode coupler/multiplexers and the like. Such devices may be provided with optical fiber pigtails which enable the connection of the device to another optical fiber. The optical fiber pigtails may be affixed to an integrated component by inserting the end of a fiber into a groove, cavity or the like, which is situated on the substrate, with the fiber core in alignment with an optical path, and gluing the fiber in place. The pigtails preferably comprise the same type of conventional coated optical fiber to which the device is intended to be connected. Some conventional fibers are provided with a relatively thick coating. A short portion of the coating is removed from the end of the optical fiber prior to attaching it to the integrated circuit. The density of optical paths that may exist at the edge of a circuit may be so great that there is insufficient space for the conventionally coated optical fiber pigtails to exist in a side-by-side array and yet have the fiber ends align with their respective optical paths. When conventional fibers having relatively thick coatings have been employed, the density of connections to the device has therefore been made small enough to accommodate such coatings.